something prevents me from backing up my computer

I've installed Norton Internet Security 2011.  I've unsuccessfully tried to fully backup my computer.  I have Windows 7 64-bit.  When I run the Windows update utility, I have Norton Internet Security 2011 in silent mode.

 

The Windows backup utility will fill up 2 DVDs - approximately 76% completed.

When the Windows backup utility asks for a third DVD, I am unable to eject the second DVD.  The program is locked.  I have to cancel the backup operation so I can get the DVD out of the computer.

 

I wonder if Norton can help?

 

Thanks, Mark.